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operation will resume. Should the load remain, the
protection circuit will continue to cycle ON and OFF at
approximately on (1) second
intervals... causing a
"popping" sound in the speaker system. Excessive loads
can be caused by grounded (shorted) speaker leads,
shorted power output transistors, etc.
2. Short Circuit Protection
This circuit provides "short circuit" protection against three
possible conditions.
A. R15 provides "hold off" bias voltage to Q13 to prevent the
amplifier converter from turning ON, except as con
trolled by the Auto Power Switch (Q18) discussed in
paragraph 1 above. The base of 013 will be about 23.3
volts when potentiometer R3 is properly adjusted.
B. Should a malfunction occur which "pulls" the positive
(+25V) side of the converter below 14 volts, Q13 will
conduct... causing 030 to charge and "cut off" the base
drive to Oil and Q12... thus turning OFF the converter.
A
typical condition which could cause the converter to
fall
below 14 volts would be an "overload" which could be
caused by a "shorted" speaker.
C. Each amplifier channel also provides a protecting
input
to 013 through R62. Should either amplifier channel
conduct more than 7.5 amps through the output driver
transistors (04 and 023), the protection transistors
(08
and 015) will turn ON, thus biasing 013 ON and causing
the converter to turn OFF. After approximately one
(1)
second, the circuit will neutralize and attempt to
turn ON
again. If the excessive load has been removed, normal
3. Voltage Regulators
Two voltage regulators supply power to the 10 Amplifier (U2).
A. VR2 and 07 serve to regulate the +25 volt converter
voltage to +18 volts for use as the positive 10 supply.
B. VR3 and 014 serve to regulate the -25 volts converter
voltage to -18 volts for use as the negative 1C supply.
Characteristic operating voltages are shown on the schematic
diagram
and
also on the
PCB
component connection
diagram. Note that the component connection diagram shows
the "reverse" (solder) side of the board, thus allowing all
troubleshooting to be performed on the solder side of the
board. All troubleshooting should be performed without
removing the board from the heat sink. Should the amplifier be
operated under load (speakers connected) while removed
from the heat sink, the power output transistors will be
damaged or fail due to excessive temperature.
3. INSTALLATION DIAGRAM
12 * FUSE
WHITE
<t=^
GACEN
TO Sftncnr
f
BLACK
BLACK
-oe
4
\7
A
TO GROUND
Fuse
CAAT
GRAY
f
Black
BLACK
4
>■
INPUT
a
AO * 360
CAR
RED
RED
>■
STEREO
Output
+
GREEN tCLLOW
LEFT
-8Q
^ '
GREEN WHITE
4"
+
GHCfN YELLOW
CRAY
YELLOW
4
>
LEFT FRONT
3 -
RIGHT
« ● BfJ
WMITE
+
LEFT REAR
2.4p
^ i
+
GRAY
T|
> >-
RIGHT FRONT
2.40
When using four speakers, connect in series as shown
at the right, such that the total impedance of the
speakers becomes 4 to 8 ohms.
+
RIGHT REAR
2-4 0
2
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